1. Field of the Invention
This invention relates to a novel process for making mercaptopropylalkoxysilanes.
2. Description of the Prior Art
Mercapto-substituted silicon compounds are known in the art. They had been made primarily by two processes. One involves the addition of hydrogen sulfide to an ethylenically unsaturated radical bonded directly to silicon. This is illustrated by the reaction of a large excess (e.g. greater than 400%) of hydrogen sulfide with a vinyl substituted silane. The other common method for manufacture of mercapto-substituted silicone compounds involves the reaction of an alkali metal mercaptide with a choroalkyl silicon compound, which results in the formation of sodium chloride by-product.
Recently, U.S. Pat. No. 4,012,403 disclosed a synthesis of mercapto-substituted silicon compounds which avoids the necessity of using such a large excess of hydrogen sulfide and which does not result in the formation of a corrosive by-product such as sodium chloride. The synthesis described in said patent is based upon the development of a method for reducing beta-cyanoethyltrialkoxysilane by reaction with sulfur. It was found that, by reacting one mole of beta-cyanoethyltrialkoxysilane at high pressure and elevated temperatures with a least three moles of hydrogen and at least one mole of sulfur in the presence of a transition metal polysulfide catalyst, one could obtain high yields of the corresponding mercaptopropyltrialkoxysilane.